Physics exam tommarow NEED HELP

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Physics exam tommarow NEED HELP!!!!!!!

hows it going, im new to this forum and want to know how to do these problems for my exam tomorrow, thanks for the help in advance lets get to the questions:

1) three vectors have x and y component vectors as shown in the table below:
what is the magnitude of the resultant vector of: s+t+U?

x y

s -2.5 +4.5

T +3.0 -1.5

U +5.5 + 5.0

the choices for the answers are A)4.9 B)24 C)10 D)18 apparently the answer is C) but i am not sure how to get that

2) a boat, whose speed in still water is 8.0m/s, is moving up a river(against the current). If the speed of the current is 6.0m/s, how far up the river will the boat be 4.0 seconds later, relative to land?

A)4.0m B)8.0 C)16.0m D) 32.0m

Not sure how to do this problem but the answer is apparently B)
 

Answers and Replies

  • #2
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3) a stone is thrown horizontally with an initial speed of 20m/s from the edge of a vertical cliff that overlooks the river below. if it takes exactly 6 seconds for the stone to reach the river, how high is the cliff? how far from the base of the cliff did the stone hit the water?

list of y values known, and a list of x values known?
Values to find:
equation(s):
show your complete solution to the problem here using the equation(s) you identified above:
 
  • #3
tiny-tim
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Welcome to PF!

hows it going, im new to this forum and want to know how to do these problems for my exam tomorrow, thanks for the help in advance lets get to the questions:

1) three vectors have x and y component vectors as shown in the table below:
what is the magnitude of the resultant vector of: s+t+U?

Code:
                 x                y

s              -2.5             +4.5

T              +3.0            -1.5

U              +5.5            + 5.0

the choices for the answers are A)4.9 B)24 C)10 D)18 apparently the answer is C) but i am not sure how to get that

2) a boat, whose speed in still water is 8.0m/s, is moving up a river(against the current). If the speed of the current is 6.0m/s, how far up the river will the boat be 4.0 seconds later, relative to land?

A)4.0m B)8.0 C)16.0m D) 32.0m

Not sure how to do this problem but the answer is apparently B)

Hi B Serious! Welcome to PF! :smile:

1) how far did you get?

What is S + T + U?

2) how fast is the boat going relative to the land?
 
  • #4
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4) you are following directions that a friend has given you to a restaurant from your home. First, you are instructed to go due South for 4.5km, then turn left onto Main Street and go east for 2.6km. at this point, you are told to take Maple Street which runs 30 degrees west of north for 4km to the restaurant. At dinner, you mention to your friends that it seems like you are almost back to where you started. They all agree so you decide to determine how far, and in what direction, you could have traveled to go straight to the restaurant. Assume no buildings or other structures will prevent you from going directly from your home to the restaurant. Include a sketch of the entire path actually traveled. Also sketch the path you could have taken to go straight to your destination.

show your full and completely documented solution here using the techniques and conventions discussed in class.
 
  • #5
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Hi B Serious! Welcome to PF! :smile:

1) how far did you get?

What is S + T + U?

2) how fast is the boat going relative to the land?

not to far......s, t, u have an arrow over each of them i guess there vectors, and for the second question all that is stated is what i posted.. not sure if that helps but thanks again
 
  • #6
tiny-tim
Science Advisor
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.. not sure if that helps …

I don't need help! :rolleyes:

I'll ask again:

1) what is S + T + U?

2) how fast is the boat going relative to the land?
 
  • #7
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I don't need help! :rolleyes:

I'll ask again:

1) what is S + T + U?

2) how fast is the boat going relative to the land?

ok i got you the boat is going 2m/s relative to the land, so you times that by 4 and you get 8
 
  • #8
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can you give me some help on the other problems
 
  • #9
tiny-tim
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3) a stone is thrown horizontally with an initial speed of 20m/s from the edge of a vertical cliff that overlooks the river below. if it takes exactly 6 seconds for the stone to reach the river, how high is the cliff? how far from the base of the cliff did the stone hit the water?

Show us what you've tried, and where you're stuck, and then we'll know how to help. :smile:
 
  • #10
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Show us what you've tried, and where you're stuck, and then we'll know how to help. :smile:

well i know that you would do 20 times 6 because the velocity would be constant throughout so the answer would be 120m/s...but im just not sure how to set up the problem with the known values and the values to find out.
 
  • #11
cristo
Staff Emeritus
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well i know that you would do 20 times 6 because the velocity would be constant throughout so the answer would be 120m/s...but im just not sure how to set up the problem with the known values and the values to find out.

This doesn't make sense: you can't just multiple numbers together willy-nilly. What are you trying to calculate here?
 
  • #12
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This doesn't make sense: you can't just multiple numbers together willy-nilly. What are you trying to calculate here?

trying to figure out the problem?????
 

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